How to terminate Python scripts in Processing framework properly?.md

From How to terminate Python scripts in Processing framework properly?

• first thing, osgeo.gdal is for pure Python scripting:

    from osgeo import gdal  
    raster  = gdal.Open('your.tif')   
    raster.GetProjection()

Everything else is a problem of osgeo, and not of PyQGIS, since you use 2 QGIS existing layers:

     ##raster_1=raster  
     ##raster_2=raster

you don't need it. To process the layers, the correct code is:

    raster_1 = processing.getobject(raster_1)   
    raster_2 = processing.getobject(raster_2)

an the crs is given by:

    new_proj = raster.crs()

• second thing, you cannot load a raster in QGIS without projection (if not yet existing, it is chosen by QGIS, according to some criteria):

So your first condition if proj is None:, is unnecessary and your script become (you don't need a list with only two layers):

    raster_1 = processing.getobject(raster_1)
    raster_2 = processing.getobject(raster_2)
    if raster_1.crs()==raster_2.crs():
         action
    else:
         WrongCRS()

and the script terminate by himself.

PS: in the last version of the processing module, it is now:

    processing.getObjects()

PS2:

For terminate the script, you can embed your script in a function and use sys.exitfunc() (I use the Python console to to see the results)

example:

    import atexit
    .....
    def all_done():
        message = '- Rasters must have the same CRS!\n\nExecution cancelled!'
        print message   
    atexit.register(all_done)
    raster_1 = processing.getObject(raster_1)
    raster_2 = processing.getObject(raster_2)
    def main():
        if raster_1.crs() != raster_2.crs():
             sys.exitfunc()
        else:
              message = "ok"
              print message
              continue
    main()

Result in the Python console: